The claimed invention relates generally to the field of disc drive data storage devices and more particularly, but not by way of limitation, to a disc drive stacked actuator having a counterbalance fastener which secures stacked components in the actuator together and which acts as a counterbalance to a flex circuit assembly mounted to the actuator.
Data storage devices of the type known as Winchester disc drives are well known in the art. Such disc drives magnetically record digital data on one or more rigid recording discs that are rotated at a constant, high speed. An array of data transducing heads access data tracks defined on the various disc surfaces to write data to and read data from the discs.
An actuator is used to controllably position the heads adjacent the discs. A typical rotary actuator is rotated about an actuator rotational axis by way of a cartridge bearing assembly affixed within a central body portion of the actuator. Rigid actuator arms project from the central body portion in a direction generally toward the discs, and flexible suspension assemblies (flexures) are affixed to the ends of the rigid actuator arms. Each flexure supports a head adjacent a corresponding data recording surface. The heads are provided with aerodynamic features that allow the heads to be supported upon a thin layer of air currents established by rotation of the discs.
A typical rotary actuator further comprises a flat actuator coil which projects from the central body portion opposite the rigid actuator arms. The coil is immersed in a magnetic field established by one or more permanent magnets and magnetically permeable pole pieces of a voice coil motor (VCM). Application of current to the coil establishes electromagnetic fields which interact with the magnetic field of the VCM to cause the actuator body to rotate about the actuator axis. As the actuator body rotates, the heads are swept across the corresponding disc surfaces to bring a selected head into alignment with a selected data track.
A flex circuit assembly is typically provided to facilitate electrical communication between the heads and coil and disc drive control circuitry. A typical flex circuit assembly comprises an array of flexible, laminated ribbons with embedded parallel signal traces that transmit coil driver current to the coil and write and read signals to and from the heads. It is common to incorporate preamplifier driver (preamp) circuitry onto the flex circuit assembly, and to mount the preamp to a side of the actuator body. The preamp generates write signals for the writing of data and preamplification and other signal processing during the reading of data.
Some disc drives of the current generation employ what is referred to as a stacked actuator configuration. A stacked actuator is formed by stacking a number of substantially planar components together to provide the final desired actuator configuration. A through-fastener can advantageously be used to clamp the various components together during the assembly process prior to insertion of the cartridge bearing assembly into the central actuator body portion.
It is generally desirable to provide a nominally balanced actuator to achieve optimal data transfer performance and external shock and vibration resistance. Disc drive designers typically attempt to align the actuator center of mass with the actuator rotational axis. Attempts are also typically made to achieve nominally symmetrical mass balancing along a centerline that passes along a length of the actuator from the coil, through the actuator rotational axis and out to the heads.
Actuator balancing is adversely affected to some degree by the attachment of the flex circuit assembly (including the preamp and associated bracketing) to one side of the actuator. Compensating for this imbalance that arises from the flex circuit assembly can be made in a number of ways. One way generally involves adding additional mass to the other side of the actuator body portion opposite the preamp to cancel the mass added by the flex circuit assembly. Another way is to cant the coil slightly about the actuator axis away from the flex circuit assembly so that a small amount of skew is provided between the actuator arm centerline and the coil centerline.
While operative to reduce actuator imbalance, these and other approaches have been found undesirable for a variety of manufacturing and performance reasons. Designers are motivated to reduce mass of the actuator to achieve faster seek times and improved control, so adding additional mass to the actuator to cancel imbalance runs counter to this goal. Canting the actuator coil so that the coil and arms are no longer in a straight line through the axis of rotation can tend to introduce vibration modes that can affect head positioning during operation, and can also increase manufacturing costs.
Accordingly, there is a continued need for improvements in the art to promote the design and manufacture of actuators which are nominally balanced, have relatively low mass and support manufacturing in an automated assembly environment.
A stacked actuator for use in a disc drive and a method of fabricating the same are disclosed. In accordance with preferred embodiments, a disc drive includes a number of discs rotatable about a disc rotation axis.
A stacked actuator comprises a plurality of stackable members including at least one substantially planar arm member which supports a data transducing head and at least one substantially planar spacer which establishes an elevational location of the arm member. The stackable members form a component stack configured for rotation about an actuator rotational axis. An external component such as a flex circuit assembly providing an electrical communication path for the head, is affixed to the component stack.
A counterbalance fastener engages the component stack to secure the stackable members together and to remove imbalance about the actuator rotational axis induced by the flex circuit assembly. The fastener preferably comprises a through-hole threaded bolt which extends through a respective fastener aperture formed in each of the stackable members to secure the stackable members together.
Preferably, the stacked actuator further comprises a cartridge bearing assembly disposed within the component stack to facilitate rotation of the actuator about the actuator rotational axis, wherein the cartridge bearing assembly is disposed between the fastener and the flex circuit assembly. The flex circuit assembly preferably comprises a preamplifier driver circuit affixed to the component stack, wherein the fastener operates to remove imbalance induced by a mass of the preamplifier driver circuit.
The method preferably comprises steps including providing a plurality of stackable members comprising at least one substantially planar arm member configured to support a data transducing head and at least one substantially planar spacer configured to establish an axial location of the at least one arm member along an actuator rotational axis; arranging the stackable members into a component stack; installing a counterbalance fastener at a fastener location proximate a first side of the component stack to secure the stackable members together; and attaching a flex circuit assembly proximate a second side of the component stack opposite the first side to provide an electrical communication path for the actuator, wherein the fastener location is selected such that a mass of the fastener operates to counterbalance a mass of the flex circuit assembly to nominally balance the actuator about the actuator rotational axis.
The method further preferably comprises installing a cartridge bearing assembly into a central bore of the component stack, the cartridge bearing assembly facilitating rotation of the actuator about the actuator rotational axis. The cartridge bearing assembly is preferably installed by providing the cartridge bearing assembly with a cylindrical outer bushing having a proximal end and a distal end, wherein a head flange radially extends about the proximal end and threads are provided on the distal end.
The cartridge bearing assembly is inserted through the central bore of the component stack so that the head flange comes into abutting alignment with the component stack, after which a carriage nut is installed onto the threads on the distal end of the outer bushing so that the carriage nut and the head flange cooperate to provide a clamping force upon the component stack. Preferably, the stackable members are arranged into the component stack such that a center of mass of an actuator coil is aligned along a centerline defined along a largest length of the at least one arm member.
By using the fastener to fasten the stack during manufacturing and thereafter as a counterbalance for the flex circuit assembly (including the preamplifier driver circuit), the fastener promotes a lower mass actuator design since additional mass need not be added to the actuator to offset the mass of the flex circuit assembly. Placing the fastener opposite the flex circuit assembly also allows use of symmetric actuator arms, which improves resonance and tilt drop performance.
These and various other features and advantages which characterize the claimed invention will become apparent upon reading the following detailed description and upon reviewing the associated drawings.